Conventionally, a thermal protector like that shown in FIG. 4 exists. In the thermal protector 1 shown in this figure, external circuit connection terminals 3 and 4 are respectively secured to both ends of a lower portion of a securing portion 2 made of an insulating synthetic resin. The ends of the external circuit connection terminals 3 and 4, which are secured to the securing portion 2, are incorporated into one body with the securing portion 2 in a form of being folded within the securing portion and respectively exposed at both ends of an upper portion of the securing portion 2, although this is not clearly shown in the figure.
To an upper exposed portion 5 of the external circuit connection terminal 3, one end 6-1 of a movable plate 6 is secured, for example, with spot welding. At the other end 6-2 of the movable plate 6, a movable contact 7, which protrudes over the lower surface, is arranged by caulking the upper surface. In the central portion of the movable plate 6, a bimetal 11 whose breadth direction is aligned by drop preventing pieces 8a and 8b, which are arranged to be erect at both sides, and whose both ends in the vertical direction are engaged in two engagement pieces 9a and 9b, which are formed to be hooked and as opposed to each other, to engage with the movable plate 6 is arranged. Additionally, on an upper exposed portion 12 of the external circuit connection terminal 4, a fixed contact 13 is arranged by being caulked. The movable contact 7 and the fixed contact 13 are arranged in positions which correspond to each other.
In this thermal protector 1, the bimetal 11 warps in a convex state in an upward direction at a temperature equal to or lower than a preset temperature, and the movable contact 7, which is supported by the other end 6-2, of the movable plate 6 made of an elastic body is pressed against the fixed contact 13 by its elasticity, so that the contacts are closed.
This thermal protector 1 is used as a temperature over-rise preventing device arranged on a flow path of hot air so as to prevent the overheating of a hot-air generating device arranged, for example, in a hair dryer, an electronic fan heater, a popcorn machine, etc. The bimetal responds to the hot air of an extra-high temperature, and the warpage in the convex state in the upward direction until at that time is inverted to the concave state in the upward direction, whereby the contacts are released, an electric current to the hot-air generating device is interrupted, and the overheating is prevented.
Conventionally, such a thermal protector is used by leaving the periphery of the contacts that open/close a power supply open as shown in FIG. 4. A member shaped like a partition wall that is arranged in the neighborhood of the movable contact 7 in some thermal protectors. However, the partition wall is arranged by necessity from an assembly viewpoint. If there is no necessity from an assembly viewpoint, the concept that the periphery of the contacts is shielded from an outside does not conventionally exist if there is no necessity from an assembly viewpoint.
A hair dryer is taken as an example. The number of recent hair dryers, which have a large capacity to emit a high volume of air (wind velocity) with high heat in order to enhance the performance as a dryer, has been growing. For such a large-capacity hair dryer that emits a high volume of air with high heat, the size of its heater must be enlarged with an increase in the size of its fan. Accordingly, the number of hair dryers where a high electric current over 10A flows in use has been becoming large.
Generally, the higher a flowing electric current or a voltage between contacts, the more an arc occurs between the contacts released when the electric current is interrupted. As described above, also in the case where an electric current as high as 10A flows at a high voltage of 100V, an arc occurs between the contacts when the electric current is interrupted. In the case of the above described large-capacity hair dryer, the energizing and the interrupt of a power supply for the heater are performed in a relatively frequent manner during its use.
The thermal protector as the above described conventional technique has one problem. Namely, as described above, a time period during which an arc that occurs between contacts when a power supply is interrupted discharges between the contacts is an instant from a macroscopic viewpoint, and an arc instantaneously occurs and disappears without being carried away by a wind even in hot air having a high rate of flow in normal cases. However, if the wind velocity exceeds a limit, an arc comes out of the contacts and is spattered to a peripheral conductive member in many cases.
Normally, the temperature of an arc is as high as several thousand degrees centigrade. Therefore, a phenomenon that if an arc between contacts is spattered to a conductive member other than the contacts even for a moment, the portion of the conductive member is extraordinarily heated and melted has been proved to occur from a microscopic viewpoint.
If a conductive member in the periphery of contacts is repeatedly melted, this causes diverse problems such as hastening the wear-out of the conductive member, causing a short circuit, or the like.
An object of the present invention is to provide a thermal protector that properly completes the interrupt of an electric current without damaging a peripheral member by an arc between contacts, which comes out of the contacts by being carried away by a wind velocity, even if a high electric current is interrupted in a large volume of air, in view of the above conventional circumstances.